1. Field of the Invention
This invention relates to a single-plate type color image pickup apparatus using a solid-state image sensor such as a CCD or the like.
2. Description of the Related Art
An image pickup apparatus may be of the kind having a single solid-state image sensor arranged to have an image of the object of shooting formed through each of color filters which transmit light of different colors and disposed one after another on each of the picture elements of the solid-state image sensor. Spatially modulated chrominance and luminance signals are formed from a signal outputted from the solid-state image sensor on which the object image is formed.
FIG. 3 shows one example of arrangement of the color filters disposed on the solid-state image sensor. In FIG. 3, reference symbols Mg, G, Cy and Ye respectively denote color filters of colors including magenta, green, cyan and yellow. The solid-state image sensor on which the color filters are arranged in this manner is operated to obtain a color signal from its output as follows.
A video signal is first outputted by scanning an even-number field and an odd-number field. At that time, in the even-number field, electric charges obtained at the picture elements (light receiving elements) of vertically adjoining horizontal lines n and n+1 are added together and the electric charges of picture elements of lines n+2 and n+3 are likewise added together.
Further, in the odd-number field also, electric charges of the picture elements of vertically adjoining horizontal lines n+1 and n+2 are added and the electric charges of the picture element of lines n+3 and n+4 are likewise added together. These added electric charges are transferred at a predetermined timing. As a result, signals having primary color components are outputted in composing ratios as shown in Table 1 below.
TABLE 1 ______________________________________ Field Line Col. Computing Formula Signal ______________________________________ even- n m Mg + Cy = R + G + 2B WB number m + 1 G + Ye = R + 2G GR field n + 1 m G + Cy = 2G + B GB m + 1 Mg + Ye = 2R + G + B WR odd- n m Cy + G = 2G + B GB number m + 1 Ye + Mg = 2R + G + B WR field n + 1 m Cy + Mg = R + G + 2B WB m + 1 Ye + G = R + 2G GR ______________________________________
Next, the four signals WB, WR, GR and GB shown above are multiplied by four predetermined coefficients to extract one of the three primary color components. Then, primary color signals of R (red), G (green) and B (blue) are obtained by the following computing processes: ##EQU1##
Since these four signals are outputted in a time sharing manner by the above-stated scanning method, they are not simultaneously obtained. Therefore, a delay element for delaying by one horizontal line, a delay element for delaying by one picture element and a selection circuit are arranged to always give the signal of the same kind.
In the case of the image pickup apparatus of the above-stated single-plate type, however, a luminance signal component is also separated from the color signal components of the four kinds. As a result, the actual color transmission characteristics of the Mg, Ye, Cy and G color filters become R, G and B transmission characteristics which differ from what is mentioned above. Therefore, there has been a problem in that the R, G and B signals obtained by the color separation process do not have an adequate color separation characteristic.